The present invention relates to a material that can be either hydrophilic or hydrophobic depending on the temperature, and to a method for obtaining said material. The present invention also relates to the use of this material for the decontamination of effluents and waste waters.
Substances displaying temperature-dependent hydrophilic or hydrophobic characteristics are known, such as thermo-reversible polymers.
Thermo-reversible polymers can shift from an initial state to a final state by either heating or cooling, depending on the initial state of the polymer. Thermo-reversible polymers, above a phase transition temperature called the Lower Critical Solution Temperature (LCST), change from a hydrophilic state to a hydrophobic state. These polymers posses a hydrophilic moiety and a hydrophobic moiety.
These polymers can find various applications, particularly for effluent decontamination.
Conventionally, for such applications, the thermo-reversible polymers can be adsorbed on suitable supports, made of glass, plastics or metal. This adsorption does not afford stable or permanent deposits or layers, i.e., a thermo-reversible polymer adsorbed on a support will not adhere sufficiently on that support.
Thermo-reversible polymers can also be polymerized in situ on a support. For example, the surface of a support can be impregnated with a monomer solution, and then this monomer can be polymerized, as described by K. Ista et al. in Applied and Environmental Biology, 1999, page 1603, or in Feng U.S. Pat. No. 5,997,961. Feng discloses a method of attaching poly(N-isopropylacrylamide) to glass surfaces which comprises the steps of (1) reacting a photosensitizer attached to a trimethoxysilane with a glass surface, and (2) photopolymerizing a N-isopropylacrylamide onto this glass surface, in the presence of a cross-linking agent. However, this method does not guarantee the adhesion and stability of the polymer layer obtained, nor does it allow a high degree of control over the properties of the polymer itself (e.g., its molecular weight, or its polydispersity, and thus its physical or mechanical properties). Besides, the use of a cross-linking agent prevents from obtaining linear chain of poly(N-isopropylacrylamide).
The use of these thermo-reversible polymers thus raises difficulties, which could be overcome by establishing a stable binding between the thermo-reversible polymers and a support, without adversely affecting the thermo-reversibility of the polymers.
It would therefore be desirable to be able to fix the polymer to the support so as to overcome the difficulties stated above.
The object of the present invention is a method that allows to obtain the grafting of a thermo-reversible polymer onto a support, in particular by a reaction that generates covalent bonds between the thermo-reversible polymer and the support.
A further object of the invention is a material that have temperature-dependent hydrophilic and hydrophobic characteristics and comprises a support having grafted thereon a layer of a thermo-reversible polymer thereon preferably by means of at least one covalent bond.
The method of the invention comprises a grafting step which is performed by means of an intermediate bonding compound that comprises (i) a first function able to react with the surface OH of the inorganic support and form with them a covalent bond, and (ii) a second function able to react with an end-function of the thermo-reversible polymer and form with it a covalent bond. The grafting method of the invention thus comprises a first step in which the inorganic support is allowed to react with at least one intermediate bonding compound, and a second step in which the support treated in first step is allowed to react with an end-function of a thermo-reversible polymer wherein the thermo-reversible polymer,
(i) results from the polymerization of a monomer of formula: 
where X is H or HO2CH3; Z and Y each represent hydrogen or a linear or branched, substituted or unsubstituted alkyl group of from 1 to 6 carbon atoms, Z and Y can be combined to form a substituted or unsubstituted heterocycle and 2 and Y cannot be both hydrogen;
(ii) has an end-function which is capable to react with the intermediate bonding compound; and
(iii) has a weight average molar mass (Mw) in the range of from 500,000 to 2,000,000.